1. Field of the Invention
This invention relates to a probe having a micro-projection and also to a method of manufacturing such a probe. More particularly, the present invention relates to a probe having a micro-projection and adapted to detect an evanescent wave used in a near field scanning optical microscope as well as a method of manufacturing such a probe. More specifically, the present invention relates to a probe having a micro-projection with a tip having a small radius of curvature, which perform well in the above application with a multiple arrangement, and which can be manufactured on a mass production basis, as well as a method of manufacturing such a probe.
2. Related Background Art
The recent invention of the scanning tunneling microscope (hereinafter referred to as xe2x80x9cSTMxe2x80x9d) made it possible to visually observe the electronic arrangement of the surface atoms of an electrocoductive specimen [G. Binnig et al. Phys. Rev. Lett., 49, 57 (1983)] so that now a real space image of a specimen is visually observable with an enhanced level of resolution, regardless if it is crystalline or amorphous. Since then, massive research efforts have been paid on the scanning probe microscope (hereinafter referred to as xe2x80x9cSPMxe2x80x9d) particularly in the technological field of evaluation of fine structures of various materials.
The SPM includes the scanning tunneling microscope (STM) adapted to scrutinize the surface structure of a specimen by utilizing the tunnel current, the atomic force, the magnetic force or the light caused there when the probe having a micro-projection is brought close to the specimen, the atomic force microscope (AFM), the magnetic force microscope (MFM) and the near field scanning optical microscope (NSOM).
Of the SPM, the SNOM is used to observe, in a non-destructive way, the surface of a specimen showing a fine pattern by means of evanescent light emitted from a very small pin-hole with an enhanced level of positional resolution of less than xcex/2 that has been unachievable by any known optical microscope.
With the SNOM, it is possible to observe a specimen of part of the body of a living thing or a cell that used to be hardly observable. Therefore, it has broadened the scope of observable specimens as well as its applications.
Three techniques are known for detecting an evanescent wave.
With a first known technique, illuminant light is applied to the surface of a specimen from the rear side in a way of allowing total reflection of light of the surface and the evanescent wave generated on the surface of the specimen by the illuminant light is detected by way of a micro-projection having a micro-aperture (E. Betzig, et al., xe2x80x9cCollection mode near-field scanning optical microscopyxe2x80x9d, Appl. Phys. Lett. 51 (25), 1987, pp2088-2090). With this technique, an image of an evanescent wave can be obtained with an enhanced level of resolution and it currently provides the most extensive theme of study.
This first technique, however, uses a sharpened glass pipette or glass fiber as a micro-projection, which is manufactured by machine-grinding. This leads to poor productivity and high production cost, and it is difficult to manufacture the aperture with good reproducibility and high precision.
With a second known technique, scattered light of an evanescent wave is detected by means of a thin film cantilever having a micro-projection with no aperture and made of silicon nitride film that is used for the AFM (N. F. van Hulst, et al., xe2x80x9cNear-field optical microscope using a silicon-nitride probexe2x80x9d, Appl. Phys. Lett. 62 (5), 1993, pp461-463).
A micro-projection to be used for the above technique may be a micro-projection of monocrystal silicon that can be prepared by using anisotropic etching that is popular in the field of semiconductor manufacturing process technology (U.S. Pat. No. 5,221,415)
FIGS. 1A through 1G show a typical known method for preparing such a micro-projection. Firstly, a pit 518 is formed by anisotropic etching in a silicon wafer 514 coated with silicon dioxide mask layers 510, 512 as shown in FIG. 1A. Then, as shown in FIG. 1B, the silicon dioxide layers 510, 512 are removed and then the wafer is coated with silicon nitride layers 520, 521 over the entire surface thereof to produce a cantilever and a pyramid-shaped pit 522 that operates as a female mold for molding a micro-projection. Subsequently, as shown in FIG. 1C, the silicon nitride layer 520 is patterned to the form of a cantilever. Thereafter, as shown in FIG. 1D, the silicon nitride layer 521 on the rear side is removed and a glass plate 530 having a saw-cut 534 and a Cr layer 532 is bonded to the silicon nitride layer 520. Then, the glass plate 530 is machined to form a mountain block 540 as shown in FIG. 1E. Subsequently, the silicon wafer 514 is etched out to produce a probe supported by the mountain block 540 and provided with a micro-projection of silicon nitride and a cantilever as shown in FIG. 1F. When it is used for a optical lever type AFM, a metal film layer 542 is formed on the top as a reflection layer as shown in FIG. 1G. This technique can produce a micro-projection showing a very acute profile at the tip and provides a high productivity and a high reproducibility.
However, an NMOS image obtained by using a micro-projection prepared by means of this second technique shows a level of resolution lower than an NMOS obtained by using a micro-projection with an aperture prepared by means of the above first technique.
While the above two known techniques provide a micro-projection to be used as an optical pickup so that an evanescent wave is detected by a photo detector comprising a photomultiplier arranged at an upper part of the micro-projection, a known third technique provides a method of directly detecting scattered light of an evanescent wave by a photodiode on a thin film cantilever (S. Akamine, et al., xe2x80x9cDevelopment of a microphotocantiliver for near-field scanning optical microscopyxe2x80x9d, Procedings IEEE Microelectro Mechanical Systems Workshop 1995, p145-150). FIG. 2 shows a cross sectional view of such a micro-projection.
Referring to FIG. 2, the illustrated micro-projection comprises a silicon thin film cantilever of a p-layer 601 supported by a silicon substrate 600 at the end thereof, a p-n junction 603 photodiode prepared by forming an n-layer 602 and Al metal wires 605 arranged on a silicon oxide film 604 to take out the signal of scattered light detected by the photodiode. An etching stop layer 606 used when preparing the cantilever is found on the lower surface of the thin film cantilever. As a result of arranging a photo detecting section of a photodiode at the free end of the cantilever, the photo detecting section and the specimen can be brought close to each other to improve the S/N ratio and the resolution of the output. Additionally, the system configuration can be simplified by this technique.
However, this third technique uses the tip of the thin film cantilever as the tip of the probe 607 and the thin film cantilever is prepared by means of a photolithography process and etching so that the micro-projection is less reproducible and it is difficult to produce a lot of products showing the same and identical tip profile if compared with the micro-projection of the second known technique.
Therefore, it is an object of the present invention to solve the above identified problems of the known techniques and provide a probe with a micro-projection that shows an improved S/N ratio and an excellent level of resolution for the detection of light or temperature and also a method of manufacturing such a probe.
Another object of the invention is to provide a probe showing a highly reproducible uniform profile and having a sharp tip that can be manufactured at reduced cost with an improved productivity and also a method of manufacturing such a probe.
According to a first aspect of the invention, the above objects are achieved by providing a probe with a micro-projection comprising:
a substrate;
first and second junction layers arranged on said substrate and electrically isolated from each other, said first and second junction layers being made of an electrocoductive material;
a micro-projection bonded to said substrate by way of said first and second junction layers and having a cavity in the inside;
said micro-projection having first and second material layers made of different respective materials and laid one on the other to form a junction interlayer therebetween, said first and second material layers being electrically connected to said first and second junction layers respectively and independently.
According to a second aspect of the present invention, there is provided a method of manufacturing a probe with a micro-projection comprising steps of:
forming a recess on the surface of a first substrate;
forming first and second material layers made of different respective materials and laid one on the other to form a junction interlayer therebetween on the surface of the first substrate having said recess;
forming first and second junction layers made of an electrocoductive material and electrically isolated from each other on a second substrate;
bonding said first and second material layers on said first substrate respectively to the first and second junction layers on the second substrate, the first and second material layers being electrically connected to the first and second junction layers respectively and independently;
separating the first and second material layers bonded to the first and second junction layers from the first substrate so as to produce a micro-projection having a cavity inside from the first and second material layers formed on the recess of the first substrate.